Thyroid Hormones

Question 1

What are the functions of thyroid hormones

Answer 1

Control normal growth and maturation.

Control oxygen consumption and regulation of lipid and CHO metabolism

Question 2

What do lack of thyroid hormones do to adults and children?

Answer 2

Lack of thyroid hormones in adults = mental and physical slowing. Children = dwarfism, intellectual impairment.

Question 3

How common is hypothyroidism?

Answer 3

common, 6 x more women than men, 1 in 10 women over age 65 has hypothyroidism.

Question 4

What are the two drugs in thyroid replacement therapy?

Answer 4

thyroxine (T4) and liothyronine (T3)

Question 5

What are the indications for thyroxine?

Answer 5

• hypothyroidism
• goitre
• replacement therapy after a thyroid block in hyperthyroidism
• thyroiditis
• thyroid carcinoma

Question 6

mechanism of action of thyroxine?

Answer 6

is a synthetic T4 thyroid hormone, replaces lowered levels of endogenous hormone. Metabolised to the biologically active T3 form.

Question 7

What are drug interactions for thyroxine?

Answer 7

warfarin, cholestyramine

Question 8

What are ADR for thyroxine?

Answer 8

ADR minimal at appropriate dose, but incl insomnia and reduced bone mineral density.

Question 9

Warnings and contraindications for thyroxine?

Answer 9

use with caution in diabetes mellitus, adrenal insufficiency, cardiac disease

Question 10

What are the indications for liothyronine?

Answer 10

it is more potent and has a shorter half life, so used for emergency and short-term relief.

Question 11

What is hyperthyroidism?

Answer 11

over-activity of the thyroid gland

Question 12

What are the goals of hyperthyroid treatment?

Answer 12

decrease thyroid hormone overproduction

block peripheral effects of excess T4

Question 13

What are the typical stages of treatment of hyperthyroidism?

Answer 13

1. antithyroid drug given - renders patient euthyroid (ie normal functioning of thyroid gland)
2. followed by surgery or radioactive iodine
3. or block and replace therapy (ie continued high dose of an antithyroid drug + replacement therapy with thyroxine)
4. Maintenance of euthyroid state

Question 14

What are drugs for hyperthyroidism

Answer 14

Carbimazole and propylthiouricel (thiourea antithyroid drugs), Iodine, radioactive iodine

Question 15

What are the dosage warnings for thyroxine

Answer 15

long half life so titrate slowly to maintenance. For elderly and ischaemic heart disease, lower start and maintenance doses.

Question 16

What is the mechanism of action for carbimazole and propylthiouricel?

Answer 16

Antithyroid (inhibit thyroid hormone synthesis by inhibiting the iodination of tyrosine residues in thyroglobulin). Propylthiouricel also inhibits the conversion of T4 to T3.

Question 17

What are the drug interactions of Carbimazole and propylthiouracel?

Answer 17

lithium, iodine, warfarin, digoxin

Question 18

What are the ADR of carbimazole and Proplythiouracel?

Answer 18

Gastrointestinal
headache'rashes
bone marrow depression
blood disturbances
symptoms of hypothyroidism in overdose

Question 19

Warnings of Carbimazole and propylthiouracel?

Answer 19

Use wtih caution if low leukocyte count
avoid if hypersensitivity to sulphur containing drugs
avoid if liver impairment
contraindicated in pregnancy